Photoconductography employing electrolytic images to harden or soften films



PHOTOCONDUCTOGRAPHY EMPLOYING ELECTROLYTIC IMAGES TO HARDEN OR SOFTENFILMS Filed July 28. 1960 Oct. 8, 1963 D. R. EASTMAN ETAL ,1

62 114 IZJQ/ //A DONALD R EASTMAN RAYMOND E RE/THEL INVENTORS Arm/ ve'rsUnited States Patent PHOTOCONDUCTOGRAPHY E M P L 0 Y I N G ELECTROLYTHCAGES T0 HARDEN 0R SOFTEN FILMS Donald R. Eastman and Raymond F. Reithel,Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey Filed July 28, 1960, Ser. No. 45,950 Claims. (Cl. 20418)This invention relates to photoconductography.

Photoconductography forms a complete image at one time or at least anon-uniform part of an image as distinguished from facsimile which atany one time produces only a uniform dot. The present invention would beuseful with facsimile but finds its greatest utility inphotoconductography.

Cross reference is made to the following series of cofiled applications:

Serial No. 45,940, iohn W. Castle, Jr., tography Employing ReducingAgents.

Serial No. 45,941, Raymond F. Reithel, PhotoconductolithographyEmploying Nickel Salts, continuation-inpart Serial No. 120,863, filedJune 7, 1961.

Serial No. 45,942, Raymond F. Reithel, PhotoconductolithographyEmploying Magnesium Salts.

Serial No. 45,943, Raymond F. Reithel, Photoconductography EmployingSpongy Hydroxide Images, continuation-in-part Serial No. 120,035, filedJune 27, 1961.

Serial No. 45,944, Raymond F. Reithel, Method for Making Transfer PrintsUsing a Photoconductographic Process.

Serial No. 45,945, Raymond F. Reithel, Photoconductography EmployingManganese Compounds.

Serial No. 45,946, Raymond F. Reithel, Photoconductography EmployingMolybdenum or Ferrous Oxide, continuation-impart Serial No. 120,036,filed June 27, 1961.

Serial No. 45,947, Raymond F. Reithel, Photoconductography EmployingCobaltous or Nickelous Hydroxide, continuation-in-part Serial No.120,037, filed June 27, 1961.

Serial No. 45,948, Donald R. Eastman, Electrophotolithography.

Serial No. 45,949, Donald R. Eastman, Photoconductolithography EmployingHydrophobic Images.

Serial No. 45,951, Donald R. Eastman and Raymond F. Reithel,Photoconductography Employing Absorbed Metal Ions, continuation-in-partSerial No. 120,03 8, filed June 27,1961.

Serial No. 45,952, Donald R. Eastman and Raymond F. Reithel,Photoconductography Employing Spongy Images Containing GelatinHardeners.

Serial No. 45,953, John J. Sagura, Photoconductography EmployingAlkaline Dye Formation, now Patent No. 3,057,787.

Serial No. 45,954, John J. Sagura, and James A. Van Allan,Photoconductography Employing Quaternary Salts.

Serial No. 45,955, Franz Urbach and Nelson R. Nail, UniformPhotoconductographic Recording on Flexible Sheets.

Serial No. 45,956, Franz Urbach and Nelson R. Nail, High ContrastPhotoconductographic Recording.

Serial No. 45,957, Nicholas L. Weeks, Photoconductography InvolvingTransfer of Gelatin.

Serial No. 45,958, Donald R. Eastman, Photoconductolithography EmployingRubeanates.

Serial No. 45,959, Donald R. Eastman and Raymond F. Reithel,Electrolytic Recording with Organic Polymers.

Photoconduc- 3&05516 Fatented Oct. 8, 1963 Serial No. 46,034, FranzUrbach and Donald Pearlman, Electrolytic Recording.

Electrolytic facsimile systems are well known. Electrolyticphotoconductography is also known and is described in detail in British188,030, Von Bronk, and British 464,- 112, Goldman, modifications beingdescribed in British 789,309, Berchtold, and Belgian 561,403, Johnson etal.

The present invention is closely related to our cofiled applicationSerial No. 45,952 listed above entitled Photoconductography EmployingSpongy Images Containing Gelatin Hardeners.

Since it involves hardening or softening of gelatin and/ or organicpolymers it is also related to the cofiled applications listed above byEastman and Reithel entitled Electrolytic Recording With OrganicPolymers, and by Urbach and Pearlman entitled Electrolytic Recording. Itdiffers from the cofiled application Serial No. 45,953 listed above ofSagura having to do with Alkaline Dye Formation in that it relates tohardening and softening of separate sheet materials. a

The present invention in certain embodiments involves the directdeposition of gelatin on a photoconductor.

In the present invention the photoconductographic image is used tocontrol the solubility of gelatin or of certain polymers coated on aseparate sheet. The object of the invention in this connection is toprovide a process which yields prints of better contrast than areobtained when the final image is formed directly on the photoconductivelayer by electrolytic deposition from an electrolyte useful inphotoconductography. Also the recording layer itself carrying thegelatin or polymer need not be electrically conducting.

Other objects of the invention depend on how the V hardened or softenedlayer is utilized. I The object of the invention thus is to provide aphotoconductographic process which produces any one of the followingresults:

The invention can also be used for making negative or positivetransparencies.

The following known phenomena are utilized in the practice of thisinvention:

Gelatin hardening: The processes of tanning or hardening of gelatin bycertain organic or inorganic chemicals are well-known reactions and arethe bases of many important photocopying and photochemical processes.Especially, some gelatin hardening agents, e.g. cobalt salts orco-polystyrene maleamic acid are effective only above a certain pHvalue. Dry layers coated from acid STAM- gel solutions are relativelyinsoluble in aqueous media above this critical pH value. STAM is theammonium salt of styrene maleamic acid copolymer and STAM and gelatindissolved in water constitutes a STAM-gel solution.

Gelatin softening (solubilization): It is also well known that aqueoussolutions of certain inorganic chemicals, e.g. potassium alum (K Al (SO-24H O) are effective hardening agents of lime-processed gelatin onlywithin a narrow pH range (pH between 3-6). Within this range, themelting point of gel layers, so hardened, is much higher than at loweror'higher pH values. Raising'the pH softens gelatin which has been sohardened. Unhardened lime-processed gelatin layers also show a markeddependence of melting point on pH but the differential is not nearly aspronounced as with potassium alum hardened gels.

Synthetic polymer solubilization: Dry layers of certain syntheticorganic polymers of the general class represented by cellulose acetatephthalate, polymethyl methacrylate comethacrylie acid, or STAM areinsoluble in acidic aqueous solutions, but can be rendered soluble inalkaline media.

Synthetic polymer insolubilization: Layers of other organic polymers ofthe class represented by polyvinyl pyridine are soluble in aqueous acidmedia but insoluble in alkaline media. Coated from acid solutions, theselayers can be insolubilized by contact with alkaline solutions.

The visibility or lack of visibility of the electro-deposited material(i.e. the image) on the photoconductive surface is irrelevant to thepractice of this invention.

This invention is essentially a two-step process in which the first stepis electrolytic and the second chemical. With various subsequenttreatments, such as wash-off, this second chemical step produces (l) aphysical change, (2) a differential in mechanical or thermo-mechanicalproperties, (3) a ditferential in dye absorbtivity, and/or (4) adifferential in receptivity to greasy" lithographic inks, when wettedwith the proper press fountain solutions.

Specifically, this invention consists of the imagewise electrolyticdeposition, on a photoconductive surface, of a material (an image)which, by itself or by chemical reaction with other agents in therecording layer, will harden or soften gelatin or insolubilize orsolubilize polymers.

The invention will be fully understood from the examples given below andfrom the following description when read in connection with thefollowing drawings in which:

FIG. 1 is a schematic fiow chart illustrating a preferred embodiment ofthe invention.

FIG. 2 similarly illustrates an alternative to one step of the processshown in FIG. 1.

FIGS. 3, 4 and 5 illustrate various printing processes utilizing thegelatin relief which results from the present invention as shown in FIG.1.

In FIG. 1 a transparency is illuminated by a lamp 11 and an imagethereof is focused by a lens 12 on a photoconductive zinc oxide in resinlayer 15 carried on a conducting support 16. The transparency is movedtothe left as indicated by the arrow 17 and the photoconductor, asindicated by the arrow 18, moves synchronously with the image of thetransparency 10.

While the photoconductivity image persists in the zinc oxide layer 15,it is passed under a brush 20 containing an electrolyte. A potentialdifference is maintained between the brush 20 and the roller 21 by asource of potential indicated schematically at 22. The zinc oxide layeris the cathode as shown, but A.C. potential may be applied since theZinc oxide in contact with the electrolyte acts as a rectifier so thatit is a cathode in the electrolytic action. The electrolyte containsmagnesium ions and an image 23 of magnesium hydroxide is deposited onthe exposed areas of the photoconductor 15. Then according to theinvention, this image is pressed into contact with a gelatin or polymerlayer carried on a suitable support 31, pressure being applied byrollers 32. The layer 30 is such that it is hardened or softened whenraised to the pH of magnesium hydroxide. In the case Where it ishardened, or insolubilized, a supply of Water 37 washes off therelatively soft or soluble areas and leaves a relief image on thesupport 31.

Alternatively, as shown in FIG. 2, when the layer 30 is a hard one,softened by the magnesium hydroxide image 23, the spray of water 37washes off the areas thus softened and leaves a relief image 38 on thesupport 31. Either of these relief images resulting from FIG. 1 or FIG.2 may be used in any of the subsequent reproduc- 4 tion processes. Forsimplicity, the relief image 35 is the one illustrated in FIGS. 3, 4 and5.

In FIG. 3 the relief image is used for imbibition printing. Animbibition dye 41 is applied by a roller to the relief image 35, forexample an image of gelatin. This relief image is then pressed into areceiving sheet 43 and the dye transfers as indicated at 44. This FIG. 3could also illustrate the use of the relief image as a spirit transfermaster. In this case the dye is applied to the relief or is included inthe original gelatin layer and in the presence of alcohol a smallportion of dye transfers to the receiving sheet. Similarly FIG. 3 couldrepresent the application of magnetic material to the relief forsubsequent use in magnetic printing.

The sheet 31 may be either hydrophilic or hydrophobic and the image 35may be hydrophobic or hydrophilic. In the arrangement shown the support31 is a hydrophobic sheet and the image 35 is a gelatin which ishydrophilic even when hardened with formaldehyde. In FIG. 4, this layerof gelatin is moistened by a roller which applies a standard fountainsolution 51. The plate is then inked with a standard litho greasy ink 53by a roller 52, the ink adhering as shown at 54 to the areas of the support 31 which are not covered by the image 35. In the usual offsetmethod this ink is transferred to an offset drum 57 as indicated at.58and is printed on a succession of sheets of paper such as shown at 59.

An alternative lithoprinting system which has proven most satisfactoryutilizes the standard litho materials (cg. Duplimat) supplied withofiice type litho presses, particularly for use with colloid transferprocesses. These standard sheets will receive and hold soft gelatinwhich, in such colloid transfer processes for making litho plates, ishardened and rendered hydrophobic. The sheet is then treated with asolution which renders the support hydrophilic, for standardlithoprinting on an ofiice litho printer such as supplied by theAddressograph-Multigraph Corporation.

In the present invention this Duplimat material is utilized withdifferentially hardened gelatin as shown schematically in FIG. 5. Thedifferentially hardened gelatin layer with hardened areas 34(corresponding to the relief areas 38 of FIG. 2) and with unhardenedareas 33 is pressed in contact with a hydrophobic litho (Duplimat)master 61, pressure being applied by rollers 69. Part of the unhardenedgelatin 33 transfers as shown at 63 to the support 61. This image istreated by swabbing with a brush 64 which applies a gelatin hardener,tannic acid, to harden the transfer image 63. The hardening in this caseis sufficient to make the gelatin hydrophobic. The whole sheet is thentreated with a solution in a brush 65 which is the standard solution(Platex) supplied with the sheet 61 to render the surface 62 thereofhydrophilic but leaving the hardened gelatin layer 63 hydrophobic. Thesupport 61 with the hydrophilic areas 62 and the hydrophobic areas 63 isnow ready for lithoprinting on a standard press, the operation beingschematically shown in FIG. 5. The moistening roller 50 applies afountain solution 51 which wets the area 62. The inking roller 53 thenapplies a greasy ink to the image areas 63, the ink adhering to theseareas as indicated at 70. Then in the usual way, the ink transfers to anoffset drum 71 as indicated at 72 and prints onto a sheet of paper 73passed in contact with the drum 71.

The gelatin relief made in accordance with the present invention may betransferred to a silk screen to act as a stencil, for silk screenprinting.

Examples of uses of solubility images are as follows:

Gelatin hardening: Since organic hardening agents such as formaldehyde,or p-quinone do not form useful electrolytic deposits (in cathodicoperation) on ZnO photoconductive surfaces, it is necessary either (1)to apply these hardening agents to an absorbent imagewise deposit or (2)to ccydeposit the hardening agent with a hydrous oxide forming material.The hardening rate and efficiency of these organic agents increases withincreased alkalinity. This alkalinity can be supplied in either or bothof two ways, (1) by the alkalinity of the image deposit and/ or (2) byadjusting the pH of the gelatin before coating.

Most of the inorganic hardening agents, e.g. potassium alum, chromealum, cerium salts, etc. which do form hydrous electrolytic depositsfrom aqueous solutions of their soluble salts do not require theinclusion of other hydroxide-forming metal salts in the electrolyticdeveloper. However, the deposition of the hydroxide of iron, forexample, is improved by the inclusion of magnesium or manganese salts inthe developer.

When the hardening agent, (e.g. co-polystyrene maleamic acid, or cobaltsalts) is ineffective in acid media, the dry layers coated from acid gelsolution containing these agents can be insolubilized by contact withalkaline reative electrolytic deposits, e.g. Mg(Ol-I) Any pigments, dyesor other materials used in the process must not detrimentally soften orharden the gelatin or polymer or adversely affect its other properties.

The following ten systems represent preferred uses of hardened gelatinrelief images:

(1) Single copy wash-off: An imagewise distribution of depositedhardening agent or hydroxy ions from an alkaline deposit it transferredby pressure contact, into a pigmented or dyed gelatin layer coated on aseparate support. The unh-ardened gelatin is removed by washing in hotwater. The resultant print is a positive if the exposure was made to anegative original. With certain gelatin layers, parts of the softgelatin adheres to the zinc oxide layer in the non-image-bearing areasto produce a direct positive image on the Zinc oxide surface; this is auseful added feature.

(2) Single copy thermo-mechanical transfer: An imagewise distribution ofhardening agent, or hydroxyl ion from an alkaline deposit, istransferred, by pressure contact, into a pigmented or dyed gelatin layeron a separate substrate. The unhardened gel is then transferred bythermo-mechanical means onto a separate receiving sheet. If thephotoconductor is exposed to a positive original, the remainingunhardened gel on the separate recording layer will be a negative copy,and the transferred gel on the receiving sheet a positive copy.

(3) Lithographic printing recording layer as master (wash-oif): Gelatinhardened with formaldehyde repels greasy lithographic inks. With the gelrecording layer on an ink-receptive substrate, a positive-to-positivelithographic printing master can be produced.

(4) Transfer to Duplimat: The unhardened gelatin is transferred, bypressure contact, onto the surface of "a gelatin-receptive MultilithType sheet and the gelatin image rendered ink-receptive by chemicaltreatment (discussed in connection with FIG. 5 above). This provides adirect positive system.

(5) Spirit duplicating: If spirit soluble dyes are incorporated in theseparate recording layer, the masters 01' prints obtained by method 1 or2 will provide a suitable duplicating master for this system.

(9) Magnetic printing: Magnetic printing masters, negative-to-positiveor positive-to-p'ositive depending on which of the above processes isused in making the relief, can be produced by incorporating magneticallyhard materials in the recording layer.

(10) Ion transfer printing: Color-forming agents incorporated in thegelatin can be transferred, by use of a suitable solvent, into anotherlayer containing other agents and upon chemical reaction form a visibleimage.

Gelatin softening (solubilization): For example, gelatin layers hardenedwith potassium alum can be solubilized, by contacting them with analkaline image deposit, by virtue of the strong dependency of hardeningefliciency upon pH. Such embodiments are particularly useful in thefollowing two examples:

(1) Single copy wash-0T: Wash-off of the softened (solubilized) areasprovides a direct-positive copying system.

(2) Single copy transfer of softened gelatin: Transfer of the softenedgel to a separate receiving sheet will provide a ncgative-to-positiveprocess.

Polymer solubilization: The dry layers of these alkaline solublepolymers, coated from organic solvent solution, can be solubilized bycontact with alkaline reacting image deposits. Even better results areobtained in this process if hydrophilic (Wettable) pigments are used inthe layer. This aids in obtaining the maximum degree of image materialtransfer and penetration. Examples, particularly which have provensuitable to this embodiment of the invention, are as follows (fourexamples):

(1) Single copy: Hydroxyl ions from an alkaline image deposit aretransferred, by pressure contact, into the dyed, or pigmented layer. Thesolubilized areas are then removed by wash-off. This furnishes adirect-positive copying process.

(2) Lithographic printing: When wetted with lithographic wet-outsolutions, the areas contacted by the alkaline image deposit will repegreasy lithographic inks. The remaining areas are ink-receptive. Thisprovides a direct-positive copying process.

(3) Stencil duplicating: A silk screen or tea-bag impregnated with oneof these polymers is contacted with an alkaline image deposit, and thesolubilized areas washed out. This provides a negative-to-positivecopying process.

(4) Magnetic printing: Incorporation of hard magnetic materials in thepolymer layers will provide a positive-topositive system for producing amagnetic printing master.

The following specific examples of the various embodi- 5 ments of theinvention were all carried outwith photocon- (6) Stencil duplicating: Agelatin impregnated silk screen or tea-bag paper (or any suitableopen-mesh material) is contacted with a hardening-agent image-deposit.The unhardened gel areas are then removed by a washoff step. Thisprovides a direct-positive system.

(7) Colloid transfer master: The unhardened dyed and/or pigmentedgelatin is transferred from the separate recording layer, bypressure-contact onto a series of suitable receiving sheets. A fewcopies can be obtained from a single master. This provides apositive-to-p-ositive system.

(8) Dye imbibition printing: The gelatin image obtained either afterWash-off or by transfer to a separate receiving sheet, will absorb dyes.As is common in dye transfer processes, these dyes can be transferredonto a separate receiving sheet.

ductive layers which consisted of dye sensitized zinc oxide dispersed ina resin binder coated on an aluminum foilpaper-laminate support usingelectrolytic development which utilizes the persistency ofphotoco-nductivity exhib ited by these layers. The invention can, ofcourse also be carried out in photoconductive processesinvolvingsimultaneous exposure and development. In all of the examples, theelectrolysis was carried out with aluminum foil backing of thephotoconductive layer held at a nega-. tive potential with respect tothe counter electrode and the electrolytic developer was carried in aviscous sponge brush-type counter electrode.

Example 1 A gelatin recording layer was prepared as follows:

6 g. Grasol Fast Black G (Gcigy dyestulfs) cc. of 2% gelatinlime-processed 6 cc. ethyl alcohol Ball mill for 18 hours in apint-sized mill with 12 Borundum balls. Filter through a balloon silkfilter bag. To 50 cc. of the above mixture was added:

50 cc. of 10% gelatin 0.4 g. KNO 1.5 cc. glycerol E Filter through aballoon silk filter bag and coat 0.005 inch thick on electron bombardedtitanox pigmented polyethylene treated paper stock.

Magnesium-formaldehyde: As one example of this invention, adye-sensitized Zinc oxide layer was exposed for seconds to 500 ft.candle tungsten illumination through a 0.3 density incrementphotographic step-wedge. The resulting conducting image was developedelectrolytically using a 1% magnesium nitrate hexahydrate plus 4%formaldehyde solution contained in a viscose sponge brush electrode,held at 70 volts, positive with respect to the zinc oxide layer with tenstrokes development. The excess electrolyte was removed from the zincoxide surface with an absorbent tissue. A sheet of the above preparedgelatin coating 0.005 inch wet thickness was moistened with cold tapwater and rolled into contact with the zinc oxide layer containing themagnesium hydroxideforrnaldehyde hardening image. After allowing 50seconds for transfer of formaldehyde and hardening to oocur, the gelatinlayer was peeled from the zinc oxide surface and the soft gelatin wasremoved by a hot water rinse (140 F.). A hardened gelatin plus dyepigment relief image remained on the polyethylene coated sheet. Astep-wedge image of soft gelatin remained on the zinc oxide layer in apattern corresponding to areas of low exposure. The hardened gelatinstep-wedge image indicated that an exposure of 125 ft.-candle-second wasrequired on the zinc oxide layer to produce hardening of the gelatinfrom a photoconductographic image produced as above. This example isalso given in our cofiled application on spongy images containinggelatin hardeners but is included here because it is not known whetherthe formaldehyde also deposits electrolytically.

Example 2 Chrome alum: As another example of this phase of theinvention, a dye-sensitized zinc oxide layer was exposed for 5 secondsto 400 ft. candle tungsten illumination through a high-contrast linenegative reversed from left to right. The conducting image was developedelectrolytically using a 1% solution of chrome alum (potassium chromiumsulfate tetracosahydrate) contained in a viscose sponge brush electrode,held at 70 volts potential positive with respect to the zinc oxidelayer, and ten strokes development. The excess developer was removedfrom the zinc oxide layer using an absorbent tissue. A sheet of thegelatin layer prepared in Example 1 was moistened with cold tap waterand rolled into contact, gelatin face to zinc oxide layer surface. Afterallowing seconds for chrome alum transfer, the gelatin layer was peelednight at room temperature, after which the final, net

from the zinc oxide layer and the soft gelatin was removed by rinsing in110 F. tap water for 10 seconds. A gelatin plugs pigment positive reliefimage of the negative was left on the polyethylene coated paper support.

For examples 3 and 4 gelatin layers were prepared in the followingmanner:

6.0 g. Grasol Fast Black G 100 cc. 2% gelatin 2 cc. ethyl alcohol Ballmill for 67 hours in a pint-sized mill using 12 Emmadum balls and add:

80 cc. 10% gelatin 20 cc. distilled water Filter through a balloon silkfilter bag and coat at pH: 6.5, pH=4.9 and pH=4.0 on titanox pigmentedpolyethylene coated paper stock BE7385C, 0.003 inch and 0.005 inch wetthickness.

Example 3.il4agnesium-Cerium A sheet of dye-sensitized zinc oxide wasexposed for 3 seconds to 400 ft.-candle tungsten illumination through ahigh contrast, line copy, negative transparency and developed as inExample 2 using a solution of 0.5% magnesium nitrate hexahydrate plus 1%cerous nitrate hexahydrate. Transfer was effected as in Example 2 usingthe gelatin layer 0.005 inch wet thickness with pH=6.5. After peelingthe layers apart, 3 minutes were allowed for hardening before the softgelatin was removed by F. tap water.

Example 4.ila'angancse-Iron A sheet of dye-sensitized Zinc oxide wasexposed and developed as in Example 3 using a solution of 0.75% ferroussulfate heptahydrate plus 0.5% manganous nitrate. Transfer was effectedas in Example 3 using the gelatin layer coated 0.005 inch wet thicknesswith pH: 4.0. After peeling the layers apart, 2 minutes were allowed foradditional hardening before the soft gelatin was removed by rinsing inF. tap water. Since it is possible that the iron as well as the hydratedoxide of manganese is being deposited electrolytically this constitutesan example of the present invention but if the iron is merely absorbedby the spongy hydrated manganese oxide image, it is an example of ourcofiled case.

Example 5C0balt As another example of this invention, a gelatin layerwas prepared in the following manner:

50 cc. 1% gelatin g. cO(NO3)2'6HgO 1 cc. glycerol 2 cc. wetting agenttap water and was rolled into contact with the above prepared magnesiumhydroxide image. Hydroxyl ions transferred to the gelatin sheet andproduced the hardening of gelatin by alkaline cobalt in 60 secondstransfer and hardening time. The layers were separated by peeling andthe soft gelatin was removed by rinsing in 120 F. tap water for 10seconds.

Example 6-ST AM A 5% STAM solution was made up as follows: Two lbs. ofSTAM (the ammonium salt of styrene maleamic acid copolymer) was stirredin 12 liters of distilled water containing cc. of a 3% NH OH solution.Stirring was continued for 2 hours and the solution was kept overweightwas adjusted to 18,160 g. with distilled water.

A dyed, alkali-hardenable STAM-gelatin layer was made up as follows:

To 200g. of a 10% de-ashed gelatin at 40 C. containing 6 cc. of 7.5%saponin, 32 cc. of the 5% STAM solution was added with stirring. Within30 seconds of the STAM solution addition, a mixture of 6 cc. of 28%acetic acid and 6 cc. of distilled water was added slowly. The entiremixture was then stirred for 20 minutes at 40 0, set by chilling andstored under 40 refrigeration. A portion of the STAM-gelatin describedabove was then remelted at 40 C. and a water-soluble dye was added.

The dyed gel was then hand-coated on a titanox pigmented, polyethylenecoated paper support with a 0.005 inch aperture doctor blade, was set bychilling and was air dried at room temperature, 50% RH. for several daysbefore use.

A piece of photoconductive, dye-sensitized zinc oxide was exposed for0.5 second to 200 ft. candle tungsten radiation incident upon ahigh-contrast negative transparency in contact with the photoconductivesurface, then brush developed at 60 volts with a viscose sponge wettedwith an aqueous solution of 1% magnesium sulfate hepta- 9 hydrate (pHadjusted to 9.6 with 2% sodium hydroxide solution). The print surfacewas then dried by blotting with an absorbent tissue.

The surface of a sheet of the dyed STAM gel recording layer wasmoistened with distilled water, then was rolled into contact with theimage-bearing zinc oxide surface. After 60 seconds, the recording layerwas peeled off and the unhardened gel areas, corresponding to the areasof no image deposit, were washedotf with 110 F. water.

Exposing the zinc oxide layer to a negative original resulted in apositive print on the recording layer.

Example 7.Lz'th0graphic Printing-Recording Layer as Master A gelatinlayer was prepared as follows:

10 F6304 100 cc. 2% gelatin 2 cc. ethyl alcohol Ball mill for 42 hoursin a pint-sized mill with 12 Borundum balls. Add 100 cc. 10% gelatin.Filter through a balloon silk filter bag and coat 0.005 inch thick onpolyethylene coated paper stock.

A dye-sensitized zinc oxide layer was exposed for 3 seconds to 400 ft.candle tungsten illumination through a positive line transparency anddeveloped electrolytically as in Example 1. (Again this may be anexample of hardening by the image or by the material in a spongy imagedepending on whether the formaldehyde is considered part of the image ormerely in the image.) A sheet of the above gelatin coated paper wasmoistened and rolled into contact with the electrolytically producedmagnesium hydroxide-formaldehyde image material. After allowing 50seconds for formaldehyde transfer and hardening to occur, the sheetswere separated by peeling. The soft gelatin was rinsed out of the imageareas with 120 F. tap water revealing the hydrophobic polyethylenesheet. The wetted formalin hardened gelatin in the background was inkrepellent. The sheet was forced air dried and mounted on a Multilith,Duplimat master and treated with Repelex fountain solution 1:32 dilutionand run on a Multilith No. 500 press usingVan Son Black No. 40904 ink.One hundred copies were made from the master.

Example 8.Spirit Master A gelatin plus spirit-soluble-dye recordinglayer was prepared as follows:

50 cc. of 5% gelatin 0.1 g. methyl violet 0.05 g. saponin It wasfiltered through a balloon silk filter bag and coated 0.005 and 0.010inch thick on polyethylene coated paper stock. A sheet of dye-sensitizedzinc oxide was exposed for 3 seconds to 400 ft. candle tungstenillumination through a high-contrast line negative. The image wasdeveloped electrolytically as in Example 1. The image is a magnesiumhydroxide formaldehyde material or is a spongy magnesium hydroxide withabsorbed formaldehyde. A sheet of the above recording layer wasmoistened with tap Water and rolled into contact with the zinc oxidelayer containing the hardening image. Fifty seconds was allowed fortransfer and hardening to occur. The gelatin layer was peeled from theZinc oxide surface and the soft gelatin was removed by a 3-second rinsein 130 F. tap water, and then was dried. A sheet of Ditto brandreceiving paper was moistened with alcohol-NaOH mixture and rolled intocontact with the gelatin plus dye image prepared above. Five secondswere allowed for transfer of dye and the receiving paper was removed.This was repeated with a second sheet etc. Ten copies were made toillustrate the multiple copy process.

Exarnple 9) for 1 /2 seconds.

Example 9.Verifax-Type Transfer Printing-Mechanical Transfer A gelatintransfer matrix was prepared as follows:

12. g. Grasol Fast Black G cc. 2% gelatin 4 cc. ethyl alcohol Ball millfor 5 hours in a pint-sized mill with 12 Borundum balls and filterthrough a balloon silk filter bag. Add 100 cc. of 20% gelatin. Filteragain and coat 0.010 inch thick on polyethylene coated paper stock.

A dye-sensitized zinc oxide layer was exposed for 3 seconds to 400 ft.candle tungsten illumination through a positive transparency line copy.The conducting image was developed electrolytically using a solution of1% magnesium nitrate hexahydrate plus 4% formaldehyde at pl-i=8.5 withsodium hydroxide as in Example 1. A sheet of the above prepared gelatinlayer was moistened with cold tap water and rolled into contact with theabove prepared image material. After allowing 50 sec onds forformaldehyde transfer andv hardening of the gelatin, the layers wereseparated by peeling and parts of the soft gelatin were transferred toVerifax copy paper by pressure rollers and peeling. Ten copies were madefrom this one master.

Example 10.Tlzernzo-Meelzanical Stripping A gelatin transfer matrix wasprepared as follows: 15 g. Fe O (ferromagnetic) 100 cc. 2% gelatin Bailmill for 52 hours in pint-sized mill with Borundum balls. Add: 1 g.Uni-Aga dispersed in 80 cc. distilled water at 75 C. 20 cc. 10% gelatin2 cc. wetting agent Filter through a balloon silk filter bag and coat0.003'

inch thick on polyethylene coated paper support.

A sheet of dye-sensitized Zinc oxide was exposed (as in The layer wasdeveloped electrolytically as in Example 9. A sheet of the abovepreparedgelatin coating was moistened and rolled into contact with the magnesiumhydroxide-formaldehyde image material. After allowing 50 seconds. forformal dehyde transfer and hardening to occur, the sheets were separatedby peeling. The gelatin coated polyethylene sheet containing the imagehardened gelatin was run through heated rollers at approximately F. incontact with a sheet of Veri-fax copy paper. The sheets were separatedby peeling and there was complete transfer of the soft gelatin to theVerifax copy paper to produce a positive reproduction, the hardenedgelatin remaining on the polyethylene coated sheet in the form of anegative reproduction. If exposure is made through a negativetransparency, the useful positive image remains on the polyethylenecoated sheet and the soft background gelatin transfers to the Verifaxreceiving sheet to produce a negative.

Example 11.--Magnetic Printing Master A gelatin plus ferromagneticpigmented recording layer was prepared in the following manner: 50 cc.of 2% gelatin (lime processed cattle-hide) 3.0 g. R2 0 (ferromagnetic) 2cc. ethyl alcohol These compounds were mixed together in a pint-s zedball mill with 12 Borundurn balls and milled for 18 hours. To the abovemixture was added:

50 cc. of 10% gelatin 0.4 g. KNO

0.5 g. Uni-Aga (from gelled concentrate) at 50 C.

It was filtered through a balloon silk filter bag and coated 0.005 inchthick on polyethylene coated stock.

The process for producing a relief image here was the same as forExample 1 except that the exposure was made through a high-contrast linenegative. The image (consisting of hardened gelatin plus E2 was airdried and was magnetized by running one pole face of a bar magnet acrossthe surface of the image material several times. The print was thenbathed in a suspension of carbonyl iron in cyclohexane for 10 seconds.The print was allowed to dry and the carbonyl iron particles held by themagnetic image were transferred between pressure rollers to a speciallytreated pressure transfer paper. A carbonyl iron positive imageresulted.

Example 12.-Gelatin Softening-Single Copy-Wash Off A sheet of the GrasolFast Black G pigmented recording layer (pl-1:49) described in Examples 3and 4, was bathed for 60 seconds with agitation in 100 cc. of a 3%, byweight, potassium alum (K Al (SO -24H G- photographic grade) solution,was rinsed briefly with distilled water, then was air dried at roomtemperature for 20 hours before use. This prehardened gel layer wasfound to be insoluble in 104 F. water.

A piece of the photoconductive, dye-sensitized zinc oxide material wasexposed for 1 second to 500 ft. candle tungsten radiation incident upona high-contrast positive transparency in contact with thephotoconductive surface and then was developed, electrolytically, at 60volts with a viscose sponge wetted with an aqueous solution containing1% by weight, magnesium nitrate hexahydrate the pH of which was adjustedto 9.5 with a 2% sodium hydroxide solution.

After electrolytic development, the print surface was dried by blottingwith an absorbent tissue which removed the excess electrolyte from thenon-image-bearing areas.

The gel surface of the recording layer was then moistened with coldwater and was rolled into contact with the image-bearing photoconductivesurface.

After 60 seconds, the recording layer was peeled off and the solubilized(softened) areas, corresponding to the areas of alkaline image-deposit,were removed by washing in running 104 F. tap water. The gelcorresponding to the areas without image deposit was unaffected by thistreatment. Exposure of the zinc oxide to a positive original produced apositive print on the recording layer.

Example 13.Single Copy: Polymer Solubilization g. of 'y-Fe o was addedto 100 ml. of ethyl alcohol in which was dissolved 5 g. ofmethylmethacrylate methacrylic acid (MMAX). The mixture was roll milledfor 24 hours in a pint-size ceramic jar containing 12 Borundum balls,then was coated on titanox-pigmented, polyethylene-coated paper stockwith a 0.003 in. aperture doctor blade and the layer air dried at roomtemperature for two days before use.

A piece of the photoconductive layer was exposed for seconds to 400 ft.candle tungsten radiation incident upon a positive transparency incontact with the photoconductive surface, and then was electrolyticallydeveloped at 70 volts with an aqueous solution of 1% by weight,magnesium nitrate hexahydrate. The surface was tien dried with anabsorbent tissue.

The surface of a sheet of the 'y-Fe O MMAX layer was wetted with waterand then was rolled into contact with the image-bearing photoconductivesurface. The areas solubilized by contact with the alkaline magnesiumhydroxide image material were then removed by washing with 140 F. tapwater. During the washing, a cotton pad was rubbed on the surface to aidin removing the solubilized areas.

Example 14.-Litlz0graplzic Master A solution consisting of 5% by weightof methylmethacrylate methacrylic acid dissolved in ethyl alcohol wasused to coat a 0.005 in. (wet) layer on :1 Mylar (poiyethyleneterephthalate) support. The layer was then air dried at room temperaturefor several hours before use.

A piece of the dye-sensitized zinc oxide material was exposed for 5seconds to 400 ft. candle tungsten radiation incident upon ahigh-contrast positive transparency in contact with the photoconductivesurface and then was elecrolytically developed at 70 volts with anaqueous solution containing 1% by weight, magnesium sulfateheptahydrate. The surface was then dried by blotting with an absorbenttissue.

The Mil TAX layer surface was then wetted with dis tilled water and wasrolled into contact with the image bearin g photocenduetive layersurface.

After 60 seconds the layer was peeled off and its surface was wettedwith a 1:7 dilution of Repelex fountain solution. The surface was thenhand-inked with Kwiklith Process Black No. 244388 carried on a plasticroller.

The areas of the MMAX layer which had contacted the image-bearing areasof the photoconductive surface were ink-repellent. The remaining areaswere ink-receptive.

Example 15.Sillc Screen A piece of silk screen was impregnated with a 3%by weight MMAX ethyl alcohol solution. The silk screen was dipped intothe solution, then allowed to air dry at room temperature for severaldays before use.

A sheet of the photoconduetive layer was exposed for 10 seconds to 400ft. candle tungsten radiation incident upon a high-contrast negativetransparency in contact with the photo-conductive surface and then waselectrolytically developed at 70 volts with an aqueous solutioncontaining 1% by weight magnesium sulfate heptahydrate. The surface wasthen dried with an absorbent tissue.

The MMAX impregnated silk screen was wetted with water, then was rolledinto contact with the image-bearing photoconductive surface.

After seconds, the silk screen was removed, and the areas solubilized bycontact with the alkaline, magnesium hydroxide image deposit were washedout with hot water. The remaining areas were unaffected by thistreatment.

The water-treated screen was then dried in forced air at roomtemperature.

An ink print was made by hand squeegeeing ink through the stencil onto asheet of ink-absorbent paper.

Example 16.-ll4agnetic Printing Master The print obtained in Example 13was used as a magnetic printing master.

The 'y-F6 O MMAX image on the print was magnetized by drawing the printacross one pole of a bar magnet.

The print was then dipped into a carbonyl iron-Freon 113 slurry. Thecarbonyl iron adhered to the imagematerial but not to the background.

The carbonyl iron was then pressure-contact transferred to a receivingsheet by passing between two steel rollers.

Example 17.-Polymer Insolubilization A polymer layer was prepared asfollows: 5 g. poly-2- vinyl-pyridine was added to 35 cc. distilled H Ocontaining 2 cc. 12 N HCl.

The mixture was allowed to stand for a period of 14 hours. Theundissolvcd material was filtered out and the following was added:

15 cc. 20% gelatin 0.5 g. 5,5 indigo disulfonic acid disodium salt 2 cc.wetting agent The material was filtered through a balloon silk filterbag and coated 0.003 inch on titanox pigmented polyethylene coated paperstock.

The gelatin merely acts as a binder and other binders may be used. Thetreatment (discussed below) with 13 Mg(OH) acts to soften the gelatinslightly; the main elfect is the hardening and insolubilization of thepolymer.

A sheet of dye sensitized zinc oxide coating on an aluminum foil paperlaminate was exposed for 3 seconds to 400 ft. candle tungstenillumination through a high contrast line-copy negative transparency.The resulting conducting image was developed electrolytically, using asolution of 1% magnesium nitrate hexahydrate (pH 9.0 With NaOl-l), heldin a viscose sponge brush electrode, 7 volts positive with respect tothe zinc oxide layer. The excess developer was removed from thephotoconductors surface with an absorbent tissue and the surfacecontaining the basic magnesium hydroxide image wetted with a thin layerof distilled water. A sheet of the dry coating made as above was rolledinto contact with the above prepared image material. After allowing 50seconds for hydroxyl ion transfer and polymer insolubilization to occurthe recording layer was peeled off and washed under warm water. Theareas rendered insoluble by the Mg(OH) were unaffected by this washtreatment, whereas the areas corresponding to the nonimage areas weredissolved off the recording layer leaving a relief image of dyedpolyvinyl pyridine.

Example 18.Electr0lyfic Deposit 0 Gelatin In some of the cofiledapplications (e.g., Urbach and Nail, Uniform PhotoconductographicRecording on Flexible Sheets) gelatin was included in the electrolyte. Asmall amount of such gelatin aids in the deposit of metal or otherimage, but not enough gelatin comes down to be useful as a relief image.ample, however, concerns the deposit of large amounts of gelatin,sufficient to be visibly dyed. We have found that gelatin containingcobalt ions or STAM-gelatin :containing magnesium ions depositselectrolytically and forms a relief image directly.

It is noted that neutral or slightly acid, aqueous solutions of cobaltsalts, e.-g., Co(NO are not effective as gelatin hardeners. However, inan alkaline medium (such as at the pH at which Co(OH) forms) cobaltbecomes an effective hardening agent. This is utilized in the presentexample.

A sheet of dye sensitized zinc oxide in resin was exposed for 1 secondto 500 foot candle tungsten radiation incident upon a high contrast linecopy negative transparency in contact with the photoconductor'. Theimagewise conductivity pattern was then developed electrolytically withan aqueous electrolyte made up of 40 cc. of a solution of 5% limeprocessed gelatin (pl-I adjusted to 8.5 with 2% NaOH) and cc. of asolution of 10% cobaltous nitrate hexahydrate.

A viscose sponge carrying the above developer electrolyte, held at 60volt positive potential with respect to the aluminum foil backing of thephotoconductor, was twice drawn slowly across the exposed surface. Thesurface was then rinsed with water at room temperature to remove any gelsolution from the nondmage-bearing areas. The image-bearing areasretained a relatively heavy gelatin relief image. The sheet was then airdried at room temperature.

For comparison with this gelatin image, another sheet of the samephotoconductor was similarly exposed and, in this case, developed in anaqueous solution of 1% cobaltous nitrate hexahydrate (but with nogelatin). It was rinsed and air dried.

One-half of each print was dipped for several seconds into an aqueoussolution of the dye 5,5'-indigo disulfonic acid disodium salt and rinsedunder cold tap water. The image material on the gelatin developed layerabsorbed the dye whereas the image developed without gelatin did notabsorb dye.

The present ex 14 Example 19 This example is similar to Example 18 butusing magnesium ions which at high pH harden STAM gelatin. The operationis the same. The electrolyte contained both magnesium nitrate and STAMgelatin. The STAM gelatin was found to deposit with the magnesiumhydroxide and to form a STAM gelatin relief image which dyed readily.

Having described various examples of our invention, it is pointed outthat it is not limited thereto but is of the scope of the appendedclaims.

We claim:

1. In a photocoductographic process in which an image pattern ofvariations in electrical conductivity is produced in a photocoductivelayer, the steps of electrolytically cathodically depositing an alkalineimage of magnesium hydroxide and placing said image directly in contactwith an organic polymer layer whose solubility in water changes in thepresence of alkaline magnesium hydroxide.

2. The process according to claim 1 in which the layer is gelatin whichis hard at a pH lower than that of magnesium hydroxide and which issoftened by said image.

3. The process according to claim 1 in which said layer is gelatincontaining a hardening agent which is effective only above a pH valuebetween neutral and that of magnesium hydroxide said agent beingselected from the group consisting of cobalt salts and co-polystyrenemaleamic acid, which layer is hardened by said image.

4. The process according to' claim 1 in which said layer is a syntheticorganic polymer selected from the group consisting of cellulose acetatephthalate and poly methyl methacrylate co-methacrylic acid whichpolymers are relatively insoluble in aqueous solutions with pH below 7and which increase in solubility at the higher pH of magnesiumhydroxide.

5. The process according to claim 1 in which said layer is primarilypolyvinyl pyridine coated from an acid aqueous solution which layer isrendered substantially insoluble at the pH of magnesium hydroxide.

6. The process according to claim 1 in which the layer is gelatin whichis differentially hardened by the image and the soft areas of whichadhere to the photoconductor to form a gelatin relief.

7. In a photoconductographic process in which an image pattern ofvariations in electrical conductivity is produced in a photoconductivelayer, the steps of electrolytically cathodically depositing chromichydroxide distributed in accordance with said pattern from anelectrolyte containing chrome alum and placing said deposited chromichydroxide directly in contact with a gelatin layer which hardens in thepresence of chrome alum.

8. Gelatin hardened by the addition of cobaltous ions at a pH greaterthan that at which cobalt hydroxide forms.

9. In a photoconductographic process in which an image pattern ofvariations in electrical conductivity is produced in a photoconductivelayer, the steps of electrolytically cathodically depositing inaccordance with said pattern an image containing a gelatin hardenerselected from the group consisting of magnesium hydroxide and chromealum and placing said deposited image directly in contact with a gelatinlayer which hardens in the presence of said hardener.

10. A process according to claim 9 in which the gelatin layer contains acobaltous salt.

References Cited in the file of this patent UNITED STATES PATENTS571,531 Langhans Nov. 17, 1896 2,763,553 Clark et a1. Sept. 18, 1956FOREIGN PATENTS 215,754 Australia June 23, 1958

1. IN A PHOTOCODUCTOGRAPHIC PROCESS IN WHICH AN IMAGE PATTERN OFVARIATIONS IN ELECTRICAL CONDUCTIVITY IS PRODUCED IN A PHOTOCODUCTIVELAYER, THE STEPS OF ELECTROLYTICALLY CATHODICALLY DEPOSITING AN ALKALINEIMAGE OF MAGNESIUM HYDROXIDE AND PLACING SAID IMAGE DIRECTLY IN CONTACTWITH AN ORGANIC POLYMER LAYER WHOSE SOLUBILITY IN WATER CHANGES IN THEPRESENCE OF ALKALINE MAGNESIUM HYDROXIDE.